Hi Krt_Bong,
If your PC is locking up then there is something more fundamental wrong than some errant/unwanted services. Software like gamebooster are something I would never ever recommend. Now it might be easy to blame CoD for this, especially if it is the only software causing lockups. The truth is that I and many others here can run CoD without lockups, this means it is most likely a system fault. Here comes the usual car anology
Imagine the red engine warning light came on in your car. Instead of bringing it to a mechanic you just put a bandaid over the light on the dashboard. You haven't actually fixed the problem, you have just hidden it from view. The fundamental problem is still there, getting worse and worse until eventually the engine dies completely. Gamebooster is the equivelant of the bandaid in this anology...
My advice is backup any important files and run a clean install of your OS. Make sure to download the latest drivers for ALL of your hardware prior to formatting, such as Motherboard, Soundcard, Video card etc. I have seen up to 50% boost in performance from PCs after they have been wiped and reinstalled. So much crud runs in the background unknown to the layman that some games/sims simply don't have enough RAM to run correctly.
Can you tell us your full system specs please?